1. Field of the Invention
The present invention relates to a protection circuit, and particularly to a protection circuit utilizing shrinkage of a heat-shrinkable device.
2. Description of Prior Art
In general, surge absorbing elements, such as metal oxide varistor (MOV), are often installed in a circuit to avoid damage caused by transient voltage surge from a power supply system. Since the surge absorbing element generates much heat when the transient voltage surge is absorbed, the surge absorbing element may be burned itself and damage electronic elements in the neighborhood of the surge absorbing element.
Traditionally, a thermal cutoff fuse is disposed between the surge absorbing elements and the power supply system. The thermal cutoff fuse is fused by heat so as to cut off circuitry between the surge absorbing element and the power supply system. When in operation, the surge absorbing element may be at a temperature higher than the temperature detected by the thermal cutoff fuse, and the surge absorbing element may be associated with a service life shorter than the thermal cutoff fuse. Thus, the surge absorbing element may be burned before the thermal cutoff fuse is fused or at the same time when the thermal cutoff fuse is fused.